1. Field of the Invention
This invention relates to apparatus and method for reproducing a signal recorded on an optical recording medium.
2. Description of the Related Art
Nowadays, an optical recording medium prevails in recording media for recording an information such as video and audio information. A write-once disc, such as CD-ROM, DVD-ROM, etc., and a write-once read-many type of disc, such as CD-R, DVD-R are available for the optical recording medium in the market. Recently, there has been suggested a rewritable disc such as CD-RW(compact disc-rewritable), DVD-RW(digital versatile disc-rewritable), etc.
As shown in FIG. 1, the DVD-RAM is divided into a data area DA for recording a user data and a header area HA pre-formatted with an identification information. The data area DA and the header area HA exist alternately in the circumferential direction of the DVD-RAM. As shown in FIG. 1B, the data area DA is provided with a groove track 10 having a concave section and a land track 12 having a convex section. These groove and land tracks 10 and 12 exist alternately in the radial direction. A recording pit train 14 is defined along a center-line of the disc at each of the groove and land tracks 10 and 12 to record a user data. A boundary side 18 of the groove and land tracks 10 and 12 is wobbled in a shape of sinusoidal-wave signal. A wobbling signal occupying a low frequency band is detected by changing a light quantity reflected by the wobbled boundary side 18 periodically. This wobbling signal is used to generate a channel clock and so on in recording mode.
The optical disc reproducing apparatus includes a recorded signal reconstruction apparatus as shown in FIG. 2 to detect a data recorded in a shape of the recording pit train 14 and the pre-pit train 16 into the corresponding pulse train. The recorded signal detector consists of an equalizer 20 and a comparator 22 connected in series, and an integrator 24 connected to a feedback loop of the comparator 22. The equalizer 20 receives a radio frequency signal RF detected by an optical pickup (not shown). As shown in FIG. 3, the radio frequency signal RF has a different amplitude depending on a length (e.g., 3T to 14T) of the recording pit and the pre-pit. Such a radio frequency signal RF is equalized by means of the equalizer 20 in such a manner to has a constant amplitude like an equalized radio frequency signal ERF in FIG. 3. The equalizer 20 controls an amplification factor in accordance with the amplitude of the radio frequency signal RF, thereby applying the equalized radio frequency signal having a constant amplitude to the comparator 22. The comparator 22 converts the equalized radio frequency signal ERF into a pulse signal PS shown in FIG. 3. To this end, the comparator 22 compares the equalized radio frequency signal ERF with a slice voltage Vsl and logicalizes the compared result. The pulse signal generated at the comparator 22 has a width corresponding to a length (e.g., 3T to 11T) of the recording pit 14 or the pre-pit 16. The integrator 24 integrates the pulse signal PS from the comparator 22 to detect an average level voltage of the pulse signal PS, that is, a direct current voltage level. Also, the integrator 24 applies the average level voltage to the comparator 22 as the slice level voltage Vsl. The slice level voltage Vsl varies in accordance with a length of the recording pit 14 and a distance ratio between the recording pits 14. Accordingly, the pulse signal outputted from the comparator 22 always has a duty ratio of 50%, and allows a user data to be reproduced accurately.
For example, a user data recorded on the disc is encoded in such a manner that a total length of the recording pits 14 included in a constant length of unit recording region (i.e., frame) corresponds to 50% the length of the unit recording region. Accordingly, when a normally recorded user data is reproduced, an average voltage level of the pulse signal PS detected by the integrator 24 has xe2x80x9c0 Vxe2x80x9d. As a result, the normal pulse signal PS identical to that upon reproduction is detected from the comparator 22 without a variation in the slice level voltage Vsl. Otherwise, the recording pits occupy a region more than or less than 50% of the unit recording region at the time of recording a data due to a recording light quantity, a rotation speed or a surrounding temperature, etc. A high logic pulse width of the pulse signal PS when a user data recorded in the unit recording region is reproduced becomes narrower and wider than a high logic pulse width of the pulse signal PS when a normally recorded data is reproduced. This results from a light quantity reflected by the unit recording region abnormally being larger or smaller than a light quantity reflected by the unit recording region normally. When a unit recording region having the abnormally recorded data is reproduced, an average level voltage detected by the integrator 24 becomes higher or lower than xe2x80x9c0 Vxe2x80x9d. As the average level voltage becomes high or low, a high logic pulse width of the pulse signal PS outputted from the comparator 22 becomes narrow or wide. As a result, a pulse signal PS having always a constant range of width(i.e., 3T to 11T) is reconstructed at the comparator 22. As described above, the slice level voltage is controlled in accordance with a duty ratio of the pulse signal PS, thereby stabbly performing the reconstruction of the pulse signal PS using the comparator 22.
As shown in FIG. 4, a high frequency component of pit train signal PTS from the recording pit train 14 and/or the pre-pit train 16 as well as a low frequency component of wobbling signal WS from the boundary side between the wobbled groove and land tracks 10 and 12 is included in a high frequency signal WRF picked up from the disc such as the above-mentioned DVD-RAM, that is, a high frequency signal picked up from the wobbled track(hereinafter referred to as xe2x80x9cwobbling radio frequency signalxe2x80x9d). Due to this, a direct current voltage level of the wobbling radio frequency signal PRF fails to have a constant voltage level (e.g., xe2x80x9c0 Vxe2x80x9d) and changes in the low frequency component of wobbling signal as shown in FIG. 4. This is caused by a fact that a high frequency component of pit train signal PTS is combined with a low frequency component of wobbling signal WS to swing in accordance with an envelop of the wobbling signal WS. On the other hand, because a high frequency signal NRF, hereinafter referred to as xe2x80x9cnormal radio frequency signalxe2x80x9d, picked up from a disc without the wobbled groove and land tracks, hereinafter referred to as xe2x80x9cnormal discxe2x80x9d, does not include the low frequency component of wobbling signal WS, it has a constant direct current voltage level(e.g., xe2x80x9c0 Vxe2x80x9d). When both the wobbling radio frequency signal WRF and the normal radio frequency signal NRF is converted into a shape of pulse signal by means of the recording signal reconstructing apparatus in FIG. 2, a pulse signal WPS, hereinafter referred to as xe2x80x9cwobbling pulse signalxe2x80x9d, derived from the wobbling radio frequency signal WRF has a length different from the length(i.e., 3T to 11T) of the recording pit 14 periodically, whereas a pulse signal NPS, hereinafter referred to as xe2x80x9cnormal pulse signalxe2x80x9d, derived from the normal radio frequency signal NRF has a width corresponding to the length of the recording pit 14. In other words, a large or small width of error is periodically generated in the wobbling pulse signal WPS. This is caused by a fact that the large-width error and the small-width error in the wobbling pulse signal WPS is canceled every a period of the wobbling signal WS to maintain a direct current voltage level detected at the integrator 22 constantly. Such a pulse reconstruction error will be more apparent from the following description with reference to FIG. 2. Referring to FIG. 5, the wobbling radio frequency signal WRF is sliced on a basis of a slice level voltage Vsl to produce a wobbling pulse signal WPS. If the normal radio frequency signal NRF is sliced on a basis of a slice level voltage Vsl, then a normal pulse signal NPS is produced. Edges of the wobbling pulse signal WPS becomes gradually distant from edges of the normal pulse signal NPS and thereafter draws gradually near to them in accordance with a change in the amplitude of the wobbling signal. More specifically, the edges of the wobbling pulse signal WPS is most far away from the edges of the normal pulse signal NPS at the peak of the wobbling signal WS. For example, at the positive peak of the wobbling signal WS, the wobbling pulse signal WPS rises at a time xe2x80x9ct1xe2x80x9d going by a time interval xcex942 from a time xe2x80x9ct1xe2x80x9d when the normal pulse signal NPS rises. Further, a deviation xcex942 between the edge of the wobbling pulse signal WPS at the peak of the wobbling signal WS and the edge of the normal pulse signal NPS becomes larger than deviations xcex941and xcex943between the edge of the wobbling pulse signal WPS at the rising portion and the falling portion of the wobbling signal WS and the edge of the normal pulse signal NPS. Moreover, a width of the wobbling pulse signal WPS becomes narrower than that of the normal pulse signal NPS at the positive region of the wobbling signal WS, whereas a width of the wobbling pulse signal WPS becomes wider than that of the normal pulse signal NPS at the negative region of the wobbling signal WS .
As described above, the conventional recording signal detector detects a pulse signal having a width different from the length of the recording pits on the wobbled track. Such a width error in the pulse signal acts as a noise component at the later signal processing stage such as the conversion of channel bit stream, thereby preventing a user data on the wobbled track from being reproduced accurately.
Accordingly, it is an object of the present invention to provide an apparatus and method for reproducing a recorded signal on an optical recording medium that is adapted to accurately reproduce a signal recorded on the optical recording medium having wobbled tracks.
Further object of the present invention is to provide an apparatus and method for reproducing a recorded signal on an optical recording medium that is adapted to accurately reproduce a signal recorded on the optical recording medium.
In order to achieve these and other objects of the invention, a recorded signal reproducing method for an optical recording medium according to one aspect of the present invention includes the steps of picking up a signal included in a signal included in the optical recording medium; detecting a specified period of signal included in the picked-up signal; and compensating for the picked-up signal on a basis of the specified period of signal.
A recorded signal reproducing method for an optical recording medium according to another aspect of the present invention includes the steps of picking up a signal included in a signal included in the optical recording medium; detecting a specified period of signal included in the picked-up signal; and reconstructing a data signal from the picked-up signal on a basis of the specified period of signal.
A recorded signal reproducing apparatus for an optical recording medium according to still another aspect of the present invention includes a pickup for picking up a signal included in a signal included in the optical recording medium; detecting means for detecting a specified period of signal included in the signal from the pickup; and compensating means for Compensating for the signal from the pickup on a basis of the specified period of signal from the detecting means.
A recorded signal reproducing apparatus for an optical recording medium according to still another aspect of the present invention includes a pickup for picking up a signal included in a signal included in the optical recording medium; detecting means for detecting a specified period of signal included in the signal from the pickup; and reconstruction means for reconstructing a data signal from the signal picked up by the pickup on a basis of the specified period of signal from the detecting means.